The present invention relates generally to the production of curved, tempered sheets of glass and, more particularly, to an improved method of and apparatus for bending and treating glass sheets having openings therethrough.
In recent years, curved glass sheets have become increasingly popular for use as glazing closures, particularly in sight openings for vehicles such as automobiles and the like. For such purposes, the glass sheets must be bent to precisely defined curvatures dictated by the configuration and size of the openings and the overall design of the vehicle.
Generally, curved glass sheets intended for use in automobiles are tempered to increase their resistance to damage due to impact and to improve the breaking characteristics of the glass when broken so as to fragment into relatively small harmless particles as opposed to the large, jagged pieces resulting from the breakage of ordinary untempered glass.
One common method of producing curved, tempered sheets of glass is to heat flat sheets of glass to their softening temperature, press the softened sheets to the desired curvature between complemental shaping surfaces and then rapidly chill the bent sheets in a controlled manner to a temperature below the annealing range of glass. Generally, these operations are carried out successively while the sheets of glass are being advanced substantially continuously along a fixed path including a heating area, a bending area and a chilling or tempering area whereby the heat initially imparted to each sheet to bring it to the proper bending temperature can also be utilized in the final heat treating or tempering operation.
Very often the glass sheets produced for movable or slidable glazings, such as automotive doorlights for example, are formed with openings adjacent at least one edge thereof for mounting on associated studs and the like constituting a part of the equipment for moving the lights between the opened and closed positions. One serious problem encountered in the production of such sheets, especially relatively thin glass sheets which are becoming more popular for automotive glazing purposes, is the occurrence of venting from the holes therein during the passage of the sheets through the blasthead when conventionally processed as described above. The reason for this venting is believed due to the relatively small areas of glass between the openings formed in the sheet and the edge thereof, which are not of sufficient mass to maintain the necessary heat or temperature required for proper tempering.